Mahinda Rajapaksa forced to abandon speech over allegations he has presided over torture and other human rights abuses

Tamil asylum seeker 'Hari' told the Guardian on Tuesday that he was tortured after being deported, including beatings on his back with electrical wire and being suspended upside down by his ankles. Photograph: Teri Pengilley for the Guardian

More than 1,000 Tamil protesters demonstrated outside a diamond jubilee lunch for the Queen in protest over the presence of the president of Sri Lanka as he was forced to abandon a keynote speech in the City of London on Wednesday.

Mahinda Rajapaksa, accused of presiding over human rights abuses after allegations of war crimes by Sri Lankan armed forces, was a guest, along with David Cameron, at the lunch in London hosted by the Commonwealth secretary general, Kamalesh Sharma.

Demonstrators descended on Marlborough House, Pall Mall, with some wielding hanged effigies of the president. Their chants echoed around the forecourt as guests arrived. Police estimated there were 1,200 protesters, though the Tamils said there were more.

The protests are over alleged war crimes and human rights abuses. One victim told the Guardian that he was left scarred and suicidal by torture, and accused the British government of forcibly deporting asylum seekers who are then tortured in Sri Lanka. The Sri Lankan said he was tortured over 17 days after being deported from the UK last year, and accused by his torturers of trying to ruin diplomatic relations with Britain by passing on allegations of other human rights abuses by state officials.

Rajapaksa was jeered as he swept through the main gates of Marlborough House in a Range Rover, which did not carry a flag because of security concerns.

The Queen spent a brief moment with the president and his wife, and the two shook hands at a pre-lunch reception in the Blenheim Saloon. Presidents, prime ministers and high commissioners from the 54 Commonwealth nations attended the event.

The Queen attended alone as the Duke of Edinburgh remained in hospital, receiving treatment for a bladder infection, where his condition was said to have improved considerably. The Queen visited him at the King Edward VII hospital, central London, after the lunch.

Rajapaksa was seated to the Queen's left, with Babli Sharma, wife of the Commonwealth secretary general, the Namibian president Hifikepunye Pohamba and his wife, and the New Zealand prime minister John Key and his wife. He later stood alongside Cameron for a "family photo" of the group, apparently arranged informally and not dictated by protocol.

Several Commonwealth states, most of them former British colonies representing two billion people, have faced criticism over human rights abuses, particularly in relation to draconian laws that criminalise homosexuality.

Rajapaksa was the main focus of protest. Earlier, demonstrators had gathered at Mansion House, in the City, where the president had been due to give the keynote speech at a diamond jubilee meeting of the Commonwealth Economic Forum. But the event's organiser, the Commonwealth Business Council, said on its website: "After careful consideration, the morning sessions of the forum … will not take place." Tickets to the event cost £795 plus VAT.

Scotland Yard said it had agreed to guarantee the president's security but the CBC had decided it was "not in their interest to stage the event" because of the policing required and the likely disruption to the City.

Fred Carver, campaign director of the Sri Lanka Campaign, welcomed the news, calling it a testament to the movement.

"It is absolutely not appropriate for President Rajapaksa to be feted by the Queen at the behest of the Commonwealth secretary general," he said. "It is likely Assad learned some lessons from the way the international community tolerated civilian casualties in Sri Lanka. What lessons will Assad learn from seeing how quickly the international community rehabilitates those responsible?"

Sen Kandiah, founder of the British Tamil Forum, said: "Common sense has prevailed. There is now enough evidence that allegations of war crimes in Sri Lanka lead directly to the president himself. That is why British government officials are reluctant to meet him. He is not welcome here."

The coalition is coming under increasing pressure to revisit a policy that suggests it is safe to return Tamils to Sri Lanka. Last week the high court halted the deportation of 40 people to the island at the last minute, citing human rights concerns.

Protests were also staged outside the British deputy high commission in Chennai, India over the Sri Lankan president's invitation to the jubilee celebrations.